An Affective Engineering Study of Vibrational Cues and Affect

7/27/2019 An Affective Engineering Study of Vibrational Cues and Affect

http://slidepdf.com/reader/full/an-affective-engineering-study-of-vibrational-cues-and-affect 1/8

An Affective Engineering Study of Vibrational Cues and Affect

When Touching Car Interiors

Louise Manfredi†, Brian Henson, Cathy Barnes, Tom Childs

Affective Engineering Laboratory

School of Mechanical Engineering

University of Leeds

Leeds LS2 9JT

United Kingdom

†[email protected]

Keywords: affective engineering, kansei engineering, touch.

Category: Research paper

INTRODUCTION

Within the field of psychology, and psychophysics in particular, the understanding of texture and the perception of it has been an exciting research field since Katz’s The

World of Touch in 1925 (Kreuger, 1989). The World of Touch underpins the view

that movement and the resulting vibrations are almost certainly needed in texture

discrimination. Bensmaia and Hollins (2003) concluded in a recent study concerning

roughness and the speed of lateral finger movement that there was a relationship

between frequency and spatial periods on the surfaces tested within the context of

roughness. In contrast, Lederman (1982) found that vibration has no service in the

perception of roughness which leaves no real conclusive evidence as to the

importance of vibration as a whole. Although much work has been undertaken in the

perception of texture, little has been undertaken in the application of textures in

product design such as this study presents.

An affective engineering study is reported in this paper in which relationships

between tactile vibrational cues and affect were examined in the context of car

interiors. The motivation behind the research was to generate hypotheses to test in

future experiments concerning how touching surface textures evokes particular

emotional responses. A variety of textures for mould decoration on otherwise

identical black plastic tiles were chosen as stimuli. Any variation in the affective

response of participants is therefore due to the surface textures of the tiles. The

context was car interiors and the demographic was males aged 18 to 26. Focus groups



were used to generate and reduce adjectives using the triad method and stimuli were

chosen using semantic mapping. The semantic differential method was used to

generate a semantic space for the tiles, which was compared with the frequency

components of the vibrations when touched. The profiles of the frequency spectra

might be responsible for the emotional responses of participants when touching

surface textures.

METHODOLOGY

Two focus groups were held to generate adjectives. All participants were unaware of

the precise purpose of the focus groups, other than that they would be asked to talk

about their attitudes and feelings about the interiors of cars, and that it would be audio

recorded. Thirteen male undergraduate students took part in the focus groups.

The first activity in each session was used as an icebreaking exercise to encourage

conversation and interaction within the group who were not familiar with each other.

They were asked to talk about cars that they liked and disliked.

In the first focus group, adjectives were generated by using the triad method on pictures of cars (Thomson and McEwan, 1988). Six images of car exteriors and 6

images of interiors were mounted on A3 boards and randomly ordered. The images

of the car exteriors were shown to the group, three images at a time. The participants

were asked the similarities and differences between the three images and their

answers were audio recorded. The group was then shown the images of car interiors

in the same way. The two sets of images were arranged in a random order again, but

this time with both interiors and exteriors within each triad. Once again, the pictures

were shown to the group in triads and they were asked the similarities and differences.

Finally, the participants were shown the all 12 images again, one at a time, and asked

to choose one adjective that best described their feelings.

The triad method was used for the second focus group study and the stimuli used were

18 parts of car interiors, such as steering wheels, which were prearranged into triads

comprising of all aspects of the interior. Participants were encouraged to feel each

stimulus and, again, find similarities and differences between them.

After the focus group studies were completed, adjectives were collected from the

session recordings. Using adjective reduction guidelines (Barnes et al, 2007),

unsuitable words were rejected and the most popular and strongest words were

retained. Emotive words were grouped by similar meaning words using an affinity

diagram. Twelve words were selected: quality, masculine, engineered, warm, cheap,

exciting, comfortable, sophisticated, relaxed, unique, sporty and fashionable. The

opposite polarity of each word was indicated using ‘not’.

The stimuli for this study were samples of mould decorations purchased from Standex

(Standex). As supplied by Standex, the samples consisted of sheets of black plastic

moulded with a number of different surface textures (Figure 1). For this experiment,

the sheets were sawn into tiles, each with a different surface texture. From the 50

available tiles, 28 were selected by the authors. This was carried out in a subjective

manner with touch being the sole discriminator. Many of the tiles provided had the



same ‘pattern’ design but different grades of roughness, so it was decided that that for

this study, all pattern types with a variety of roughnesses be used.

The tiles were placed inside a black box, which had a front entrance with a small

window through which the participants could feel a section of each surface. The

boxes were black to match the colour of the tiles; none of which could be seen. This

ensured that the results yielded were based wholly on the tactual qualities of the tiles.

To reduce the number of stimuli, three semantic mapping exercises were carried out

against axes reading cheap-expensive, relaxing-exciting, each with two participants

who had not taken part in the focus groups. The participants who were asked in pairs

to determine where on the map they would best place the tiles, numbered 1 to 28 with

regards exclusively to the way the tile felt when touched. Each tile had a

correspondingly numbered marker to be placed on the map. The participants were

permitted to revisit their initial decisions and revise them if required and tile markers

could be placed on top of each other. The students were asked during the study to

keep the theme of car interiors in the forefront of their minds throughout the decision

making process. A photograph was taken of each of the completed maps and they

were compared. Tiles that were similarly placed on each of the three maps and arange of tiles from each of the maps’ quadrants were selected. This resulted in eleven

tiles (Table I).

Semantic differential questionnaires were prepared using the adjectives selected from

the focus group sessions. The words were presented in a random order and with

random polarity. Fifty seven male participants aged between 18 and 16 were

recruited in small groups to rate their subjective response to the eleven tiles on the

questionnaire. This activity took place in a controlled environment in a special

purpose affective evaluation room. Each group was read the same introduction sheet,

explaining the purpose of the study and what they were required to do. Incentives

were given as a token of appreciation. They were asked to fill out a practise sheet

with tiles not part of the experiment in order to familiarise themselves which the style

of questionnaire. The participants were asked to complete the questionnaire in silence

so not to disturb or influence the opinions of other participants. The data from the

semantic differential questionnaires was transcribed twice to spreadsheets, compared

and corrected. Missing responses were replaced with average values. The data was

analysed using principal components analysis in SPSS 14. Varimax rotation was used

and components with an eigenvalue greater than 1 were retained. The positions of the

tiles in semantic space were calculated.



Figure 1. Standex mould decorations.

Table I. Stimuli used in semantic

differential study

Tile Standex no.

1 MT 9022

2 MT 9015

3 MT 90974 MT 9081

5 K9000G

6 MT 9124

7 MT 9002

8 MT 9112

9 MT 9049

10 MT 9080

11 MT 9030

The tiles were mounted on a Kistler piezo-electric force measurement platform that

could respond to frequencies in sliding friction force up to at least 1kHz. Vibrationmeasurements of the 11 tiles were obtained by the principal author pulling the left-

hand index finger in a continual motion across each tile from right to left at a speed of

between 5 and 10 mms-1

. The data was captured from the Kistler measurement

apparatus on LabView recording 1000 times per second. Each data set lasted for

approximately 7 seconds. MatLab was used to apply a fast fourier transform to the

vibration data to give a graphical representation of the frequency spectra of the tactile

vibrations. The autocorrelation plots and the frequency spectra were then compared

with the positions of the tiles in semantic space.

RESULTS

At first, the principal components analysis was unable to generate a positive definite

correlation matrix. This was resolved by removing the averages for the word

‘fashionable’ from the analysis, because it correlated highly with the word

‘sophisticated’. Subsequent analysis identified three components (Table II).

Component 1 accounted for 49.2% of the variance; component 2, 25.8%; and

component 3, 14.0%. The words that loading most highly on component 1 were

‘exciting’ and ‘unique’; on component 2, ‘quality’ and ‘sophisticated’; and on

component 3, ‘warm’. The semantic space is illustrated in Figures 2 to 4.

The frequency spectra of the vibrations that occur when a finger is moved across the

surface of each texture are shown in Figures 5 to 15. The ordinate axis on each graph

is relative amplitude.



Table II. Rotated component matrixComponent

1 2 3

Quality -0.165 0.929 -0.094

Masculine 0.476 -0.491 0.691

Engineered 0.743 -0.153 -0.104

Warm -0.207 0.001 0.952

Cheap -0.210 -0.787 -0.095

Exciting 0.870 0.332 0.293

Comfortable -0.828 0.524 0.079

Sophisticated -0.111 0.901 -0.180

Relaxed -0.811 0.557 -0.033

Unique 0.947 0.145 -0.025

Sporty -0.544 0.675 -0.420

-2

-1

0

1

2

3

4

-2 0 2 4 6

5

7

910

1

8

11

3

4

6

2

PC 1

PC 2

Figure 2. Stimulus loadings incomponents 1 and 2.

-2

-1.5

-1

-0.5

0

0.5

1

1.5

-2 -1 0 1 2 3 4

6

2

4

3

7

9 118

10

1

5

PC 2

PC 3

Figure 3. Stimulus loadings in

components 2 and 3.

-2

-1.5

-1

-0.5

0

0.5

1

1.5

-2 -1 0 1 2 3 4

811

6

2

9

10

4

1 3

5

7

PC 1

PC 3

Figure 4. Stimulus loadings incomponents 1 and 3.

Figure 5. Spectrum of tile 1.Figure 6. Spectrum of tile 2.



Figure 7. Spectrum of tile 3.











DISCUSSION

The plots of the frequency spectra (Figures 5 to 15) for each surface differ from each

other in a number of ways. They can be characterised by:

• The number and distinctiveness of frequency peaks.

• The extent to which frequency peaks exist above 1.8Hz.

• The steepness and radii of the curves that results if a line is drawn connectingeach frequency peak.

• The frequency of the maximum peak.

• The range and relative amplitude of low frequency (>0.5Hz) components.

Consideration of the relationships between the positions of the stimuli in the semantic

map and their frequency spectra is notable for how surfaces with similar spectra elicit

different responses, and for how surfaces with different spectra can elicit similar

responses.

Against component 1, which is characterised by feelings of uniqueness and

excitement, surfaces 2 and 11 appear at opposite ends of the response scale, but have

very similar spectra. On the other hand, surface 6 is close to surface 2 in component

1, but they have very different spectra. Surfaces 2 and 6 are only similar in the range

of low frequency components, but surface 11 is also similar in this respect. Surfaces

1, 4, 5 and 11 evoke a low response against component 1, and are very similar in the

distinctiveness of their frequency peaks and the presence of frequency peaks above

1.8Hz, but if this might indicate a relationship then the position of surface 2, which

also shares these attributes, is anomalous.

Against component 2, surfaces 5 and 2 appear at opposite ends of the response scale,

but have very similar spectra. These two surfaces differ in that surface 2 has a more

pronounced frequency peak close to 0.7Hz, and so does surface 4, which is close to

surface 2 in semantic space. It is difficult to conclude a relationship between theheight of the peak at about 0.7Hz and feelings of quality and sophistication for those

surfaces close together and in the mid-range of component 2, because it is unlikely

that the variance of the responses will allow discrimination of the positions of the

stimuli in semantic space (although the authors have yet to perform this analysis).

The importance of the height of the 0.7Hz peak remains an issue for further testing.

Almost all the surfaces tested demonstrate a peak at between 0.6Hz and 0.8Hz and it

remains to be determined how this arises from the interaction of the finger and the

material from which the surfaces are made.

Component 3 is particularly interesting because of its association with feelings of

warmth. All the tiles were made of the same material and so the effect of thermal

conductivity, even when taking into account the difference in finger to surface contactarea because of different profiles, is likely to be very small. The response might be

accounted for by the other connotations of the word ‘warm’ associated with comfort

and safety, or psycho-physical perception of warmth may depend to some extent on

the profile of the surface.

Surfaces 6 and 7 evoked high responses against component 3. They are similar by not

having distinctive peaks of high relative amplitude. Surface 5, which evoked low

feelings of warmth, does not share these properties. On the other hand, surface 2 does



not share these properties either, but is close to surfaces 6 and 7 in semantic space

against component 3. Nevertheless, the hypothesis that the presence of distinctive

peaks does not elicit feelings of warmth can be tested in further research.

Other properties of the surface profiles, such as roughness and autocorrelation, remain

to be measured.

CONCLUSIONS

An affective engineering study is reported in which relationships between the

frequency spectra of tactile vibration and affect were examined in the context of car

interiors. A semantic space was generated for surface textures on otherwise identical

black plastic tiles. Vibration measurements were taken when a finger was moved

across each of the surfaces, from which frequency spectra were calculated. The

frequency spectra were compared with the tiles’ positions in semantic space.

There were no clear relationships between the frequency spectra and the tiles’

positions in semantic space. The comparisons suggest the following research

questions which could be tested in future work.

1. Whether there is a relationship between relative amplitude of a frequency peak at between 0.6Hz and 0.8Hz and feelings of quality and sophistication.

2. Whether surfaces with few distinctive frequency peaks of high relative amplitude

feel warmer than surfaces with more distinctive, higher amplitude peaks.

ACKNOWLEDGEMENTS

This work was funded by the UK’s EPSRC (EP/D060079/1) and the EC

(NEST 043157). The views expressed here are the authors’ and not those of the EC.

REFERENCES

Barnes, C.J., Delin, J., Lillford, S. P., Sharoff, S. (2007). Linguistic Support for

Concept Selection Decisions. Artificial Intelligence for Engineering Design, Analysis

and Manufacturing, 21(2), pp.123-135.

Bensmaia, S. J. and Hollins, M. (2003). The vibrations of texture. Somatosensory &

Motor Research, 20(1), pp.33-43.

Kreuger, L. E. (1989). The world of touch by David Katz. Edited and translated by L.

E. Kreuger. Hillsdale: Lawrence Erlbaum Associates, Publishers.

Standex Engraving Group. http://www.standexengraving.com/ Accessed 4 April

2007.

Taylor, M. M., Lederman S. J. (1975). Tactile roughness of grooved surfaces: a model

and the effect of friction. Perception and psychophysics, 64, pp489-494.

Thomas, D. M. H., McEwan J. A. (1988). An application of the repertory grid

method to investigate consumer perceptions of foods. Appetite, 10, pp181-193.

An Affective Engineering Study of Vibrational Cues and Affect

Documents

Transcript of An Affective Engineering Study of Vibrational Cues and Affect